1. Field
The present invention is related to wireless communication and more particularly, an apparatus and method for controlling uplink transmission power in a multiple component carrier system.
2. Discussion of the Background
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and IEEE (Institute of Electrical and Electronics Engineers) 802.16m technology are under development as candidates for the next generation wireless communication technology. The IEEE 802.16m specification not only supports compatibility with legacy systems by relying on a revision of the existing 802.16e specification but also secures continuity towards a future technology meant for the next generation IMT-Advanced system. Therefore, the 802.16m specifications are required to meet advanced requirements for the IMT-Advanced system while maintaining compatibility with Mobile WiMAX systems based on the 802.16e specifications.
Most wireless communication systems make use of one frequency band for data transmission. For example, the 2nd wireless communication system uses a frequency band in the range of 200 KHz to 1.25 MHz while the 3rd wireless communication system uses a frequency band ranging from 5 MHz to 10 MHz. To support ever-increasing transmission throughput, the latest 3GPP LTE or 802.16m is increasing frequency bandwidth up to 20 MHz or more. Increasing bandwidth is essential to deal with high transmission throughput, but large power consumption is caused to support large bandwidth even when required communication service quality is low.
In this regard, a multiple component carrier system is emerging, which defines a carrier having one frequency band and a center frequency and enables broadband transmission and/or reception of data through multiple carriers. In other words, by using one or more carriers, narrow and broad band are supported at the same time. For example, if a carrier uses a bandwidth of 5 MHz, a maximum of 20 MHz can be supported by utilizing four carriers of the same kind.
One way for a base station to utilize the resources of a user equipment in an efficient manner is to utilize information about power of the user equipment. Power control technology is essential to minimize inference factors for efficient distribution of resources in wireless communication and to reduce battery consumption of a user equipment. A user equipment can determine uplink transmission power according to scheduling information such as Transmit Power Control (TPC) allocated by a base station, Modulation and Coding Scheme (MCS), and frequency bandwidth.
Since uplink transmission power of a component carrier has to be taken into account in a comprehensive manner as a multiple component carrier system is introduced, power control of a user equipment becomes more complicated. This complexity can bring about a problem in view of maximum transmission power of the user equipment. In most cases, the user equipment should operate based on the power lower than maximum transmission power within an allowable range. If a base station performs scheduling requiring transmission power more than the maximum transmission power, actual uplink transmission power may exceed the maximum transmission power, leading to a problematic situation. This is so because power control of multiple component carriers is not explicitly defined or information about uplink transmission power is not fully shared between the user equipment and the base station.